Emission stabilized electronic valve



Sept. 26, 1950 D. G. C. HARE EMISSION STABILIZED ELECTRONIC VALVE INPUT as OUTF UT grwm vtm Patented Sept. 26, 1956 UNITED STAT m EMISSION STABILIZED ELECTRONIC VALVE Donald G. O. Hare, Greenvale, N. Y., assignor to the United States of America as represented by the Secretary of the Navy ApplicationJanuary'25, 1945, Se1'ial-No.'574,592

'1 Claims. (c1.179 171 This invention relates to vacuum-tube amplifiers, and more particularly to amplifiers stabilized against output variations due to changes in cathode emission of the vacuum tubes'used asthe amplifying means. I

In vacuum tubes, changes in cathode emission may be caused by variations in the filament supply voltage resulting in changes in the cathode temperature, or by variations in the emissive characteristics of the cathode due to irregularities in the material of "which it is made; In general, such changes in the cathode emission, however produced, cause changes in the plate current of the-vacuum tube and" consequently in the output potential developed across any load connected in the plate circuit. Such output changes may, be similar in all respects to those produced by variations in. applied signal.

If spurious outputs of the type considered above occur in the first vacuum tube of an amplifier, they cannot be eliminated by feedback circuits involving subsequent stages because there is no way. .of, discriminating between plate-current variations due to actual signals applied to the control grid of the vacuum tube, and entirely similar variations due to changes in the cathode emission of the vacuum tube. Accordingly, the vacuum tube of a single-stage amplifier or the first vacuum tube. of a multistage amplifier may introduce spurious outputs which cannot be com-, pensated by previously known means.

-In view of the above, there is proposed a vacuum-tube amplifier comprising a vacuum tube The accompanying drawing is a schematic diagram of. an emission stabilized amplifier according to the invention.

In the amplifier of the drawing, a vacuum tube l3-of the pentagrid typeis'employed in the first or only stage. This vacuum tube may, for example, bea-type 6L7- or 1612 coniprising cathode I2, plate li'andfive grids hereinafter referred to bynumbers i-through grid! being that nearest the cathode, grid 5 being that-nearest the plate,

etc. i Y r Cathode i2 is connected to ground while plate It is connected through load resistor It to a source of positive potential indicated as battery it; Grid lis connected through'resistor 20 and bias battery 22togroun'd, the polarity of battery 22 being so chosen that grid 1 is maintained positive: in respect to the cathode. Grids 2 and l are connected together and operate as a screen, being connected to asuitable source of positive potential. Conveniently, this source of positive potential may be plate battery it, and grids 2 and 4 may be connected to a suitable tap thereon. Grid 5 is connected to cathode ['2 as in the conventional suppressor grid connection.

Grid 3 is connected through bias battery and return resistor 26 to grid l, bias battery 24 being arranged normally to maintain grid 3 negative in respect to grid 5. Input signals applied between terminals 28 appear across bias battery 24 and return resistor 26, and are applied between grids l and 3. The variations in the plate potential appear between output terminals 30 connected respectively to the plate and to ground.

Considering the operation of the vacuum tube, it will be recalled that grid l is maintained positive, while control grid 3 is biased negatively in respect to grid l. Grids 2 and 4 are operated as a screen. Thus grid 2 accelerates electrons from the cathode similarly to a space charge grid and, together with grid t, provides electrostatic screening between'control grid 3 and the other elements of the vacuum tube. Grid 5 which is connected 20," increasingthe drop across that resistor and makingpoint 32 less positiveiri respect to ground; Similarly ahecrease in emission from cathode l2 resu1ts"iri point 32"'be'c'oming more positive respect to ground;

Sincereturn resistor 26 is co'nnected'to point 32",it will be seen thatthe negative potential 'd'e velope'd' across resistor 20' is applied to grid 3"in' serieswith the input signal. The result of the actionjust. descriliedis that an increase in e'rhis sion' from cathode l2 causes grid 3 to become more negativein respect to the cathode, while a decrease'in cathode emission has the opposite effect.

The stabilizing action of'the system of the invention is thus two-fold. As the cathode emission increases, more electrons are drawn ofi by grid 1 tending partially to stabilize or at least to reduce variations in the density of the electron streamreaching control grids. In addition, the fiow of these additional electrons through resistor 20 causes control grid 3 to become more negative in respect to the cathode, thereby reducing the number of electrons reaching the plate. In each case the reverse action occurs when the cathode emission decreases. It will be understood, therefore, that if the resistors 20 and 26 and the potentials of batteries 22 and 24 are properly chosen, the stabilizing action produced by grid 3 in response to variations in the current drawn by grid I will compensate exactly for the variations in emission, the plate current being maintained substantially constant for a constant input signal.

In one case, using a type 6L7 vacuum tube, plate voltage was maintained substantially constant for variations in heater voltage between and 8 volts, the input signal being held constant during the measurement.

In conclusion, it will be understood that, while the foregoing description represents a preferred embodiment of the invention, changes in the construction and arrangement of parts may occur to those skilled in the art without departing from the spirit and scope of the invention as defined in the appended claims.

Having thus fully described my invention, I claim:

1. In a vacuum tube including at least a cathode, a first grid adjacent said cathode, control grid and plate elements, means for continually stabilizing the tube for variations in electron emission from said cathode comprising an input circuit connected across said first and control grids, means for deriving a potential which is dependent upon and which varies with variation in said electron emission from said cathode, and means for applying said potential to said control grid.

2. In a vacuum tube including at least a cathode, a first grid adjacent said cathode, a negatively biased control grid and plate elements, means for continually stabilizing the tube for variations in electron emission from said cathode comprising an input circuit connected across said first and control grids, means for deriving a potential which is dependent upon and which varies as said electron emission varies, and means for applying said potential to said control grid in such manner that an increase in electron emission causes said control grid to become more negatively biased with respect to said cathode, and vice versa.

, 3. In a vacuum tube including at least a cathode, a first grid adjacent said cathode, a control grid, and a plate, means for stabilizing said tube for variations in electron emission from said cathode comprising an input circuit connected across said first and control grids, a resistor and D. C. source of potential connected in series between said cathode and first grid to bias said first grid positively with respect to said cathode, and. a second resistor and second D. C. source of potential connected in'series between said control grid and said first grid to bias said control grid negatively with respect to said first grid and cathode whereby any change in electron emission from said cathode will efiect a compensating change in the negative bias on said control grid.

4. In a vacuum-tube amplifier, an input stage comprising a vacuum tube having at least a cathode, a first grid adjacent said cathode, control grid and plate elements, input connections whereby a signal to be amplified may be applied across said first and control grids, output connections whereby the amplified signal appearing at the plate may be applied to an external circuit, and means for continually stabilizing the vacuum tube for variations in emission from the cathode thereof, these means including means for deriving a negative potential which is dependent upon and which varies with the emission from said cathode and means for applying the negative potential to the control grid.

5. An emission stabilized electronic tube including at least a cathode, a first grid adjacent to said cathode, a control grid, and a plate, means for applying an input signal across said first and control grids, means for biasing said first grid positive with respect to the cathode, means for biasing said control grid negative with respect to said first grid, and means for deriving a potential which varies with variations in said electron emission, the said potential acting to alter the bias between the first and control grids so as to compensate for the aforementioned variations in emission.

6. An electronic tube continually stabilized for variations in electron emission including at least a cathode, a first grid adjacent to said cathode, a control grid, and a plate, means for applying an input signal across said first and control grids, a resistor and direct current source of potential connected in series between said cathode and first grid to bias said first grid positive with respect to said cathode, means for biasing said control grid negative with respect to said first grid, said above-mentioned resistor drawing grid current to derive a potential which varies with variations in electron emission, said potential acting to alter the bias of said control grid so as to compensate for said emission variations.

7. An electronic tube continually stabilized for variations in electron emission including at least a cathode, a first grid, a control grid, and a plate, means for applying an input signal between said first and control grids, means connected between said control and first grids to bias said control grid negative with respect to said first grid, a resistor and direct current source of potential connected in series between said cathode and first grid to bias said first grid positive with respect to said cathode, grid current fiowing through said resistor to derive a potential which varies with variations in electron emission from the cathode, said derived potential acting to vary the potential of the common connection between the two biasing means whereby the bias of the control grid varies to. compensate for said emission variations.

DONALD G. C. HARE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,228,868 Briebrecher Jan. 14, 1941 2,273,987 Pineo Feb. 24, 1942 2,302,866 Hunt Nov. 24, 1942 2,308,997 Miller Jan. 19, 1943 2,375,877 Thompson May 15, 1945 2,392,416 Sorensen Jan. 8, 1946 2,399,441 Krebs Apr. 30, 1946 FOREIGN PATENTS Number Country Date 337,155 Great Britain Oct. 30, 1930 108,950 Australia of 1939 526,869 Great Britain M--- Sept, 26, 1940 

